The rate of material transport in and out of the cell is dependent on the **volume** of the cell. A larger cell (more volume) takes a longer time to transport materials from one point to another.

On the other hand, a smaller cell (less volume) takes a shorter time to transport materials from one point to another. This efficiency is the reason why cells are generally very small in size.

A

The process of cell division always results in the formation of **two daughter cells**. Cell division involves the duplication of DNA and the physical division of cytoplasm into two distinct cells.

The formation of two daughter cells is important in order to prevent the cell’s DNA from being overloaded. It also improves the efficiency of material transport by reducing the cell volume.

C

Each chromosome consists of two sister chromatids that are joined together at the centromere.

B. centromere

After mitosis, two identical cells are produced with the same original number of chromosomes of the parent’s cell. In this case, if a cell has 12 chromosomes, each daughter cell will have 12 chromosomes after mitosis.

C. 12

The beginning of mitosis, which is called prophase, the chromatin starts to condense and forms chromosomes. Each sister chromosome consists of two sister chromatids that are joined together at the centromere.

C. chromatids

In prophase, the chromatin starts to condense into chromosomes. This is when the spindle starts to form as the centrioles begin to separate.

A. prophase

The metaphase of mitosis is characterized by the positioning of the chromosomes at the center of a cell. They are arranged along an imaginary plane called the *metaphase plate*.

Among the given choices, the diagram in letter **B** illustrates the arrangement of chromosomes along the metaphase plate. This diagram best represents metaphase in cells.

B

Cyclin is a protein found in cells under mitosis. This protein triggers cell division and it is mainly responsible for the timing of the cell cycle in eukaryotes.

B. cyclins

External regulators, which are the proteins that respond to the activities that occur outside the cell, are mainly responsible for instructing the cells to either speed up or slow down a cell cycle.

A. speed up or slow down the cell cycle

Cancer is a disorder in which the body’s cells could no longer control growth or cell division. As a result, these cells replicate uncontrollably and form tumors, which are masses that can damage other tissues that surround it.

A. cancer

The four stages of cell division or mitosis include prophase, metaphase, anaphase, and telophase. In prophase, which is the first stage, the chromatin starts to condense into chromosomes. This is when the spindle starts to form as the centrioles begin to separate and the nuclear envelope breaks down. In metaphase, which is the second stage, the chromosomes line up in the center of the cell. Each of the chromosomes is connected to a spindle fiber. Next, the chromatids get separated and the chromosomes are moved apart. This stage is called anaphase. In telophase, the chromosomes go to the opposite ends of the cell. As a result, two nuclear envelopes start to form.

A cell relies on the instructions on its DNA in order to perform most of its functions. However, as the cell grows, more information needs to flow from the DNA, which places a larger demand.

If the cell becomes too large, the information on the DNA would not be able to keep up with the demands of the cell. This results in DNA overload, which can only be resolved by cell division.

Therefore, the risk of DNA overload is the reason why the size of a cell is limited by its DNA. In order to continue functioning properly, the cell needs to reduce its size by dividing into two.

Since the cell volume increases rapidly than its surface area, the ratio of surface area to volume will decrease. This would create a serious problem when it comes to the exchange and movement of materials. If the cell would get larger, getting sufficient oxygen and nutrients, as well as expelling waste would be very difficult to sustain.

Before a cell begins to divide, its chromosomes are first replicated into two copies, one for each daughter cell. Once the chromosomes are replicated, they begin to condense and coil tightly.

The tightly coiled chromosomes are then arranged at the middle of the cell prior to the separation of sister chromatids. Once the mitotic spindle is properly connected, the chromatids separate.

The separated sister chromatids are then moved at opposite poles of the cell. After cytokinesis, these chromatids now become less condense as they perform their function in new cells.

Interphase is the stage that occurs before the cell division. This serves as the in-between period of growth as the cell prepares for its division. Once the cell has gone through interphase, it is now ready for mitosis.

Interphase is the stage that occurs before mitosis or cell division. It is when cell growth, DNA replication, and preparation for cell division take place. It consists of three phases – the G1 phase, the S phase, and the G2 phase.

Before relating DNA, chromatid, chromosome, and centromere to each other, let us define what each term means:

DNA – found in the nucleus; contains the genetic material of a cell
chromatid – two identical parts of a chromosome
chromosome – threadlike structure that is made up of two sister chromatids
centromere – it is the point where the two sister chromatids are attached

Here is a sample explanation showing how the terms are related to each other:

A chromosome is made up of deoxyribonucleic acid (DNA) that is tightly coiled around proteins. Each chromosome consists of two sister chromatids, which contain two identical copies of DNA, that are joined together at the centromere.

A chromosome is made up of deoxyribonucleic acid (DNA) that is tightly coiled around proteins. Each chromosome consists of two sister chromatids, which contain two identical copies of DNA, that are joined together at the centromere.

•Prophase, metaphase, anaphase, telophase

•in prophase, the centrioles separate while chromosomes condenses and the spindle appears

•in metaphase, the chromosomes line up in the center of the cell while microtubules connect each chromosome to a pole of the spindle

•in anaphase, the centromeres that join the sister chromatids split while the sister chromatids separate and become individual chromosomes

•in telophase, the chromosomes after being distinct and condensed uncoil and disperse while the nuclear envelope forms again

The process of cell division always involves the replication of the cell’s chromosomes into two exact copies. Each copy would then be segregated into each daughter cell as the cell divides.

To illustrate, if a cell originally has 10 chromosomes, then DNA replication would yield 10 pairs of chromosomes, with a total of 20 chromosomes. As the cell divides, each daughter cell receives 10 chromosomes from each duplicated pair.

Therefore, the number of chromosomes in the new daughter cells is *always the same* compared to the number of chromosomes in the original cell. Cell division thus maintains DNA fidelity.

The cell cycle includes interphase and mitosis. Interphase is the stage of cell growth, DNA replication, and preparation for cell division. After interphase, mitosis occurs. It is the division of a parent cell into two daughter cells. In turn, each of the two daughter cells will undergo the same cycle again.

When cells are removed in the center of a tissue culture, they begin filling the empty spaces. Once the empty spaces are completely filled with cells, they will stop producing new ones and return to their normal state. This event indicates that when cells come into contact with other cells, they usually stop their growth.

Cyclin is a protein found in cells under mitosis. This protein triggers cell division and it is mainly responsible for the timing of the cell cycle in eukaryotes.

If cell growth in a multicellular organism is not regulated carefully, then the cells would grow uncontrollably and form masses of cells or tumor. This condition leads to cancer, which is considered the disease of the cell cycle because cancer cells fail to respond to any external regulator and internal regulator that ensure an orderly cell growth. Eventually, cancer may lead to death.

Both cancer cells and normal cells have nucleus. However, cancer cells fail to respond to any external regulator and internal regulator that ensure an orderly cell growth. As a result, they form masses of cancer cells and invade other tissues in the body. On the contrary, normal cells would listen to regulators and stop their growth to avoid damage to nearby tissues.

Temperature is considered as a primary factor which affects the rate of a cell development. Here is a sample experiment to determine whether temperature can affect the rate of mitosis.

Problem: Does a low temperature affect the rate of mitosis?

Hypothesis: Low temperature decreases the rate of mitosis.

Method:
1. Get three tomato plants which have the same height and put them in three identical pots.
2. Put plant A in a greenhouse that has an ideal temperature of 25 degrees Celsius.
3. Put plant B in a greenhouse that has a temperature of 38 degrees Celsius.
4. Put plant C in a greenhouse that has a temperature of 8 degrees Celsius.
5. Water the plants with the same amount of water for 14 days.
6. Record the height of the plants every day at the same time.
7. Compare the results.

This is an animal cell that is under the metaphase stage. This cell contains centrioles in the opposite sides of the cell. Since plants do not possess centrioles, they are only found in animal cells. This cell is currently in metaphase because the chromosomes are lined up in the center and each of the chromosomes is connected to a spindle fiber.

Considering that the cell division is the splitting of a parent cell into two daughter cells, the two strands that are attached to the chromosomes on both poles resemble the identical genetic information that they carry. Having two identical copies of the DNA is an important part of cell division because the new daughter cell must be the exact copy of the parent cell; hence, it must have the same genetic information and the same number of chromosomes.

One of the most important steps in the cell cycle is **cytokinesis**. It involves the physical separation of the cytoplasm of a cell into two daughter cells, thus completing the cell cycle.

If the cell fails to undergo cytokinesis, then the result would be a cell that contains multiple nuclei. The presence of two or more nuclei in the cell can be harmful and may cause cell death.

Therefore, it is important that a mitotic cell undergoes cytokinesis in order to separate the nuclei into daughter cells. This way, each new daughter cell would have exactly one nucleus.

Plants and animal cells both undergo mitosis. However, the difference between the cell division of plant cells and animals is the way in which cytokinesis happens. In plants, a new cell wall is formed between the two new daughter cells, whereas in animal cells, the cell membrane of the parent’s cell forms a cleavage to produce two new daughter cells. In addition, plant cells do not have centrioles. They are only present in animal cells.

Since nerve cells lack centriole, they are unable to undergo mitosis and divide to form new cells; hence, they are called amitotic. For this reason, nervous system injuries can permanently damage or cripple a person due to their nerve cells’ inability to heal or regenerate.

Each eukaryotic organism has a specific number of chromosomes that dictate the genetic information that is unique to each organism. Cell division maintains this pattern per generation.

If the number of chromosomes is altered between daughter cells in the process of cell division, then the daughter cells will either have too much or too less genetic material. Both of these conditions may be harmful to the cell and the organism.

An excess or missing chromosome can result in the development of genetic disorders. Thus, it is important that cells maintain the correct number of chromosomes for each generation.